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A Metallurgical Investigation of the Effects of Double Tempering on the Hardness, Impact Toughness and Microstructure of AISI 4140 Steel

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Low alloy steels are commonly used in industry for a wide range of applications that require high strength and toughness. Each application requires specific properties. In order to modify the alloy’s properties to meet these specifications, a variety of heat treatment techniques are employed, including annealing, quenching, and tempering. Tempering is a metallurgical process by which toughness and ductility are improved. This procedure is conducted by heating the as-quenched martensitic steel to temperatures in the ferrite plus cementite phase region for several hours. Tempering is generally carried out in a single cycle temperature-time. However, the procedure may be conducted in two cycles with cooling to room temperature between the cycles. This process is known as double tempering. The goal of this project is to investigate the effects of single versus double tempering on the mechanical properties and microstructure of 4140 steel. To achieve this goal, samples of 4140 steel were quenched and tempered at 300, 400, 500, and 600 ºC for the same total heat time in single and double tempers. The samples were machined to ASTM standard impact testing. The Rockwell hardness and Charpy V-notch impact energy were measured. The microstructure was characterized using optical and scanning electron microscopy (SEM), and carbides were extracted from each sample and XRD was used to determine their size and geometry. The results are analyzed using the Holloman – Jaffe parameter

  • This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review.
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Identifier
  • E-project-042618-161410
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Year
  • 2018
Date created
  • 2018-04-26
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Last modified
  • 2020-12-27

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